The invention relates to a molded case low-voltage limiting circuit breaker comprising a rotary contact bridge, a pair of stationary contacts cooperating with said contact bridge, a conductor for current input to each of the stationary contacts extending in the plane of movement of the contact bridge and shaped to form with the contact bridge a looped trajectory to generate electrodynamic repelling forces, a bar having a transverse opening in which there is located the central part of the contact bridge with a freedom of rotation in the opening direction due to the action of the electrodynamic forces against an elastic force providing the contact pressure, the current input conductor being arranged as a half-loop having a first and a second parallel strand spaced apart, the first strand bearing a stationary contact part.
The current limiting effect by a circuit breaker of the kind referred to depends on the speed of opening of the contacts. Regardless of the operating mechanism, this speed of opening depends on the intensity of the electrodynamic repelling forces and on the weight of the mobile assembly, i.e. the contact bridge. The small weight of the mobile contact bridge presents an unfavorable effect on closing of the circuit breaker. The contact resistance, and therefore the temperature rise, is greater. Moreover, the dispersion of the contact resistances is much greater. Correct operation of the circuit breaker can be affected by these increased dispersion and resistance phenomena and object of the present invention is to enable an improved contact device to be achieved.
According to the document EP-A-28740, a magnetic circuit presents a transverse part having a small thickness with respect to the air-gap separating the central part from the bottom strand of the current input conductor. This part of the magnetic current presents a certain flexibility liable to give rise to bouncing of the movable contact on the stationary contact, when the weight of the movable contact is small.
According to the document DE-B-1,227,978, an insulating shim is inserted without clearance between the two strands of the current input conductor. This shim does not rest on any stop of the case.